Solid-state laser systems are typically used in laser resonators for generating laser radiation. The laser-active solid (laser crystal, laser disk) is thereby optically excited by means of a pumping light source in order to generate a population inversion in the laser-active solid material.
Various measures are known for fixing the solid to the heat sink. The solid can be attached to the heat sink by, for example, adhesive bonding, soldering or by mounting with indium. A common feature of these known measures is that a filler material (for example the adhesive, the solder or the indium) remains between the solid and the heat sink. However, the use of a filler material leads to an additional thermal resistance and thus to an additional temperature difference between the contact faces of the heat sink and of the solid. Moreover, such filler materials can be damaged, for example, by the (pumped) laser radiation. If the solder is deformed or the adhesive evaporates, for example, this can lead to disadvantageous changes in the laser system. Other techniques for fixing solids to heat sinks generally require joining temperatures which can compromise the functional efficiency of coatings, in particular of reflective coatings, on the solid.
The maximum possible gain of the laser-active solid is influenced by the so-called amplified spontaneous emission (ASE), which is also referred to as superluminescence. The term ASE refers to the (unwanted) amplification within the pumped laser volume of radiation (i.e. photons) generated by spontaneous emissions in the laser-active solid, which propagates inter alia in the lateral direction. If this radiation is not coupled out of the laser-active solid to a sufficient extent, the excitation of unwanted laser modes in the solid may occur. Such laser mode(s) resulting from amplified spontaneous emission constitute a parasitic transverse radiation, which has negative consequences for the laser process. These negative effects include, for example, overheating of the solid, as a result of which the maximum achievable laser power is reduced. There can also be thermo-mechanical damage to the solid. The latter occurs, for example, as burn-offs, particle flaking or melting of the solid material.